A biological study of Durvillaea antarctica (Chamisso) Hariot and D ...

153
Table 7.5 Frequency of D. antaY'ctica specimens infected VJi th
He:Y'podiscu.s.
Size class (m) Percentage infected Percentage with hl~h
in~ection
0.0 -
005 -
l.0 ....
2.0 -
3.0 -
4,0 -
0.5 22.8
LO
2.0
29.2
3.0 41.1
4.0 72.1
5.0 95.4
21.9
11. 7
68.0
71.0
Small uninfected specimens grew the fastest (curve "A", Big.
7..14) •
Their mean length increased more-or-less linearly by 205%
in 26 months - a mean monthly increase of 7.9%. Medium sized,
uninfected plants also grew rapidly (curve "B", Fig. 7.14), reaching
176% in 18 months. However, unlike small specimens, the growth rate
of these medium sized plants decreased sharply in the 1974 winter.
Small infected specimens grew relatively slowly (curve "A",
Fig. 7.13).
A peak value of 75% was reached after 18 months, but
an abrupt decline during the late \'linter and early spring of 1974
meant that the overall growth after 26 months was only 22% (0.B5% per
month) .
The mean length of medium sized, infected specimens (curve
"B", Fig. 7.13) increased during the 1972-73 summer, but started to
decline in the autumn, so that after 26 months mean length had decreased
60%. The length of large, infected specimens increased less than 10%
in 26 months.
During the summer their frond length incyeased slightly.
but during late winter and early spring their growth '~ate
declined"
Thus D. antarctica specimens infected IIJith HeT'podiscus grew more
sl~Jly
than those uninfected.
With many infected pla.nts, ti6sue loss
far e~ceeded
production.
(e)
For several reasons, no clo~e comparison could be made bet:lIleeY}
the groillth rates of marked. D. anta::f'ctica and D. !V-il Zana plants. The
relatively sID;;J.ll number of tagged D. l;)iUana plants meant that it was
)'Jot possible to segregate this species into several size classes for